Thursday, April 01, 2010

I’m a huge fan of pranks, but I usually approach April fool’s day with some apprehension. It’s not that I mind making a fool of myself. It’s more anticipating that moment of confusion before you figure out the joke that I don’t like—like the moment just before you realize the source of the annoying beep is an annoying beeper that someone hid in your office…Although if it’s a good joke it’s totally worth it.

Physics, and most other subjects, can be like that. Who hasn’t had that moment of confusion before “seeing the light” that lasted for hours, days, weeks, or even years? (Although, like a good prank, it’s totally worth it in the end.)

Recently I read an article by Leigha Dickens, an undergraduate student that attended the joint APS/AAPT meeting as a student reporter. Reflecting on meeting Vera Rubin, whose work with Kent Ford provided the first hint of the existence of dark matter, Erin wrote,

[Vera Rubin] told us how envious she was of all of us, because we would go on to learn and discover the things she did not yet know…And that sums up both the privilege and the bane of being a scientist. We do, especially at conferences like these, get to experience something of the breadth of what human beings have learned about our world and our universe, which grows steadily year by year, and encompasses more fascinating things than one lifetime alone could spend in awe over discovering. And yet the more we discover, the more we realize what remains that we don't yet know, what we won't be able to know until more scientists and fresh insight come along to uncover it.I wonder, and I certainly hope, that the mysteries of dark matter are solved, the elusive Higgs found, and any potential climate crises averted with new and more sustainable technology, within my lifetime. Yet by the time any new discoveries come to pass, I'm sure there will be even more fascinating questions to explore.

In the 1960s, Vera Rubin and Kent Ford set out to determine the distribution of mass in the Andromeda galaxy. Their plan was to observe the time it took stars at varying distances from the center of the galaxy to rotate around the galaxy. Since the pull of gravity weakens predictably with distance, stars on the edge of a galaxy should rotate slower than those near the center. Knowing the differences in rotation time would enable them to determine the distribution of mass.

But, like many good science stories, things didn’t work according to plan. After observing dozens of spiral galaxies, Rubin and Ford were convinced that a major piece of the puzzle was missing. Contrary to prediction, stars on the outside of a galaxy moved at the same speed as stars near the center for no observable reason.

Enter dark matter.

In a spiral galaxy, the ratio of dark-to-light matter is about a factor of ten. That's probably a good number for the ratio of our ignorance-to-knowledge. We're out of kindergarten, but only in about third grade. --Vera Rubin

We still don’t know what dark matter actually is, but really, the unknown is what science is all about. Considering all that I know I don’t know, April fool’s day doesn’t seem quite so bad. Bring it on.